Aseptic food products are produced by heating the food product in a sterile environment to a predetermined temperature for a length of time sufficient to eliminate pathogens; that is, microorganisms that can cause spoilage of the food product. The food product must then be transferred to and stored, for example, in a sterile container or package to prevent the reentry of microorganisms over time. Conventional aseptic processing systems typically employ a continuous sterile flow path, including holding tanks, pumps, heat exchangers for both heating and cooling and packaging machinery.
The time necessary at a given temperature for processing a container or unit of food for the purpose of sterilization is measured in terms of an f-value, which is the equivalent time in which a product is held at temperature T to reduce microbial populations. The term f.sub.o indicates the time in minutes required to destroy a given number of organisms of a reference strain at a temperature of 250.degree. F. when the Z value is 18.degree. F. A Z value is the number of degrees Fahrenheit required for a specific death curve to pass through one log cycle (i.e., change by a factor of ten). An f.sub.o of three minutes has been found to be a safe minimum public health sterilization value for low acid food products. When the pH of a food is between 4.6 and 6.0, the f.sub.o may be reduced to between one and two minutes.
In current aseptic processing systems, all components of a food product are heated to the same temperature for the same amount of time. Temperature level and time are dictated by the food component that requires the highest temperature and the longest period of time to cook to achieve an acceptable level of sterilization required by public health standards. This requirement leads to overcooking of some components because different components react to temperature levels and cooking time in various ways, depending upon the exact makeup of the components of the product.
Current aseptic processing systems typically process food products containing large particulate components to the system at a relatively slow rate using a typical f.sub.o of 60 (sixty minutes at 250.degree. F. or its equivalent). Food products containing minor particulates, or liquid, such as sauces, can be processed at relatively fast rates using a typical f.sub.o on the order of 6.0 (six minutes at 250.degree. F. or its equivalent). Thus, when products containing a large particulate component, for example, chunks of meat, are subject to heating at high temperatures for relatively long periods of time to sterilize the large particulates, other components, such as sauces and vegetables, may undergo undesirable changes in flavor, color, texture and may lose nutrient value.